1. Field of the Invention
This invention relates to a new and improved method for desulfurization of oil stock, e.g. residual oil. More particularly, it relates to a solvent extraction method for preparing a low-sulfur, high-metals content raffinate and a high-sulfur, low-metals content extract from residual oil.
2. Description of Prior Art
It has been proposed to improve the salability of high sulfur and metal content residual-containing petroleum oils by a variety of hydroprocessing methods, e.g. hydrodesulfurization and hydrodemetalation. However, difficulty has been experienced in achieving a commercially feasible catalytic hydroprocessing process. Short catalyst life in such processes is manifested by inability of a catalyst to maintain a relatively high capability for desulfurizing charge stock with increasing quantities of coke and/or metallic contaminants deposited thereon which act as catalyst poisons. Satisfactory catalyst life can be obtained relatively easily with distillate oils, but is especially difficult to obtain in desulfurizing residual oils, since the asphaltenic or porphyrinic components of an oil, which tend to form disproportionate amounts of coke, are concentrated in the residual fractions of a petroleum oil, and since a relatively high proportion of the metallic contaminants that normally tend to poison catalysts are commonly found in the asphaltene components of the oil. Further, on a commercial scale, these processes are rather costly due to high hydrogen consumption levels. It is, therefore, advantageous to provide a desulfurization process such as the present invention which exhibits superior characteristics including good desulfurization benefits and no hydrogen consumption.
U.S. Pat. Nos. 3,716,479 and 3,772,185 propose demetalation of a hydrocarbon charge stock by contacting the charge stock with added hydrogen in the presence of a catalyst material derived from a manganese nodule.
British Pat. Nos. 1,318,941 and 1,318,942 teach use of zinc, magnesium, beryllium or calcium aluminate spinels combined, after calcination, with a Group VIII metal, such as, for example, platinum, as a dehydrogenation catalyst.
Demetalation of hydrocarbon fractions is taught in U.S. Pat. No. 2,902,429 as contacting said fractions with a catalyst having a relatively small amount of a sulfur-resistant hydrogenation-dehydrogenation component disposed on a low surface area carrier, i.e., a carrier with a surface area of not more than 15m.sup.2 /g, and preferably not more than about 3m.sup.2 /g. Examples of such low surface area carriers include diatomaceous earth, natural clays and Alundum.
Methods for separation of aromatics from paraffins or naphthenes are known in the art. See, for example, U.S. Pat. Nos. 2,109,157; 2,724,682; 2,758,141; and 3,222,416. However, the present invention is a method for separation of sulfur-containing components from the metal-containing components in a residual oil by extraction even though both types of components are generally aromatic in nature.
There are numerous references in the art showing various metals combined with carriers such as alumina, silica, zirconia or titania as catalysts for use in demetalation and/or desulfurization processes. No references are known to the applicants which teach the present invention with its attendant benefits.